1. Field of the Invention
The present invention relates to a sliding-type bearing for rotary machines, suitable particularly for use in high-speed rotary machines.
2. Description of the Prior Art
Generally, the shaft of a high-speed rotary machine is supported by sliding-type bearings each having a sliding surface provided with two lubrication oil supplying grooves formed at portions thereof substantially perpendicular to the direction of application of weight of the shaft. In this type of bearing, it is important to suppress the rise of temperature of the oil film for maintaining the performance of the bearing. As a matter of fact, however, it is extremely difficult to directly measure the temperature of the oil film. Therefore, practically, the temperature of the oil film is estimated from the actually measured temperatures of the bearing at a plurality of preselected points around the bearing surface.
The temperature of the bearing of the kind described usually exhibits a tendency as explained below.
Namely, the circumferential temperature distribution of the bearing, starting from the position of the oil groove remoter from the portion of minimum bearing clearance (This minimum clearance is determined by the direction of rotation of the rotary shaft and the direction of load) and measured in the direction of rotation of the shaft, is such that the bearing temperature is higher at the position of the oil groove (point of 0.degree.) remote from the load point than at the position of the oil groove (point of 180.degree.) closer to the point of load, i.e. closer to the point of the minimum bearing clearance. The highest bearing temperature is observed at portions around the point of 90.degree. from the above-mentioned starting point. Also, the bearing temperature at the point of 180.degree. is substantially equal to the temperature of the lubrication oil entering the bearing. Therefore, as the rotation speed of the rotary shaft is increased, the temperatures at the oil groove remoter from the load point and at the point 90.degree. apart from this oil groove in the direction of rotation are raised inconveniently. Particularly, a high temperature exceeding the maximum allowable temperature is often generated at the point of the maximum temperature. As the maximum allowable temperature is exceeded, the bearing surface is softened to reduce the mechanical strength, often resulting in a seizure between the rotary shaft and the bearing surface.
The rise of the bearing temperature is substantially equivalent to the temperature rise of the oil film. As the oil film temperature rises, the viscosity of the latter is lowered to cause a destruction of the oil film to incur the seizure.
Various countermeasures can be taken to overcome the seizure between the shaft and the bearing: (a) to lower the oil temperature at the bearing inlet, (b) to increase the oil pressure, (c) to increase the bearing clearance, (d) to provide a cooling jacket, and so forth. The measure (a), however, requires a larger capacity of the oil cooler, while the method (b) necessitates an oil pump operable at a high delivery pressure, resulting in a raised cost of the lubricating system. The method (c) incurs a larger amplitude of the vibration of the rotary shaft, while the measure (d) impractically complicates the bearing construction. Thus, as a matter of fact, there has been no practically usable measure effective to avoid the seizure between the rotary shaft and the bearing.